1. Field of the Invention
This invention relates to an expandable coiler mandrel for coiling sheet metal and the like.
2. Description of the Prior Art
Expandable coiler mandrels are frequently used in rolling mills for metal strip and sheet, recoiler equipment and the like. A strip is coiled tightly onto the expanded segments of the mandrel and can be removed later from the mandrel by moving the segments inwardly.
A typical conventional construction for a mandrel has a core, a plurality of radially expandable segments mounted around the core and, for each segment, a plurality of hydraulic piston-and-cylinder units by which the segments are movable radially, these being connected to the hydraulic units within the core.
Such a mandrel is shown in U.S. Pat. No. 2,321,146; other examples are French Pat. Nos. 1,074,746 and 2 310 950. A variation shown in French Pat. No. 1 367 531 has wedges which push the segments outwardly, the wedges themselves being moved by a piston-and-cylinder unit. In all of these, the piston units act to move the segments outwardly against the force of inwardly acting return springs, which cause retraction of the segments when the hydraulic pressure is released. The segments are not fixed to the pistons. This means that the fluid has to overcome the force of the springs in order to expand the pistons. Additionally, this mixture of hydraulic and mechanical operation is a complication and is liable to lead to vibrations or oscillations.
Another problem unsolved by the prior art is that of tilting of the segments, if for instance one piston jams or is faulty. In the above specifications, a common hydraulic feed to all pistons is shown.